NOT APPLICABLE
NOT APPLICABLE
NOT APPLICABLE
The present invention relates generally to broadband communications, and more particularly to a method and circuitry for implementing demodulator circuits.
There is a growing acceptance of video services, such as video on demand, and an anticipated deployment of home servers. As a result, broadband appliance manufacturers have an increasing need to support multiple simultaneous channels of digital content delivered over the cable system. This need includes other systems such as satellite and terrestrial TV systems. The ability to simultaneously demodulate potentially all of the channels viewed by a particular home can fundamentally change the viewing paradigm for video content from one that is driven by network schedules to one that is driven by consumers independent of networks.
FIG. 1 is a simplified high-level block diagram of a traditional multi-channel cable and satellite demodulator 100 of a type that is used in cable and satellite systems. A multi-channel RF input signal typically includes a plurality of RF channels, each characterized by a different carrier frequency and being modulated in accordance with desired information to be carried on that channel. Each channel""s bandwidth is less than the spacing of the carrier frequencies. For example, carrier frequencies in the UHF band (300 MHz to 3 GHz) may be spaced at 6 MHz intervals. Included are receiver chains 102a, 102b, and 102c. Each chain includes a tuner 110, an analog-to-digital converter (ADC) 120 and a digital demodulator 130. Digital demodulator 130 includes a forward error correction (FEC) circuit (not explicitly shown).
The function of each tuner 110 is to select an RF channel falling within a specific frequency band. There is one tuner for each RF channel. The input RF signal for a tuner contains many or all RF channels. Each tuner then converts the frequency of its selected RF channel to a lower fixed frequency pass band for cable systems, or to baseband for satellite systems. Each ADC 120 then digitizes the selected RF signal. Then each digital demodulator 130 performs signal demodulation and outputs recovered digital bits with error indication signals.
Each RF channel requires one analog tuner and analog band-pass or low-pass filters. The problem with this approach is that the cost, power consumption, and complexity go up as the required number of RF channels goes up.
The present invention provides a method and circuitry for demodulating signals such as downstream signals. At least some embodiments are characterized by lower cost, lower power consumption, and/or lower complexity.
A digital multi-channel demodulator circuit according to an embodiment of the invention includes a frequency-block down-converter that receives a multi-channel analog RF signal and shifts the multi-channel analog RF signal to a lower frequency band. An ADC receives the multi-channel analog RF signal from the frequency-block down-converter and converts the multi-channel analog RF signal to a multi-channel digital RF signal. A digital channel demultiplexer receives the multi-channel digital RF signal from the ADC and demultiplexes the multi-channel digital RF signal into separate digital RF channels.
Other embodiments include a digital selector that receives the separate RF channels and selects one or more RF channels, and a plurality of demodulators that receive one or more of the RF channels from the digital selector and demodulate one or more of the RF channels.
Other embodiments include a digital tuner for use in multi-channel demodulation. The digital tuner includes a numeric control oscillator (NCO) that generates a select frequency, the select frequency being associated with a corresponding and separate RF channel. A complex multiplier receives the multi-channel digital RF signal and multiplies the multi-channel digital RF signal with the select frequency and passes the result through a low-pass filter LPF to extract the signal that is superimposed on the corresponding RF channel.
Other embodiments include a polyphase channel demultiplexer for use in multi-channel demodulation. The polyphase channel demultiplexer includes at least one low-pass filter (LPF) configured to receive the multi-channel digital RF signal and to synchronize the RF channels. Also included is a discrete Fourier transform circuit (DFT) that demultiplexes the multi-channel digital RF signal into separate digital RF channels.
Embodiments of the present invention achieve their purposes and benefits in the context of known circuit and process technology and known techniques in the electronic and process arts. Further understanding, however, of the nature, features, and advantages of the present invention is realized by reference to the latter portions of the specification, accompanying drawings, and appended claims.